[time-nuts] Wavecrest DTS-2077 Teardown

Ed Palmer ed_palmer at sasktel.net
Wed Aug 21 16:44:24 EDT 2013


Since you're looking for rise times in the low or sub nanosecond range, 
why wouldn't you include any logic gates where such rise times are 
inherent?  I was thinking of maybe a chain of faster and faster logic 
gates.  For example, Potato Semiconductor - no, I'm not making that up - 
PO74G04A has a risetime of < 1 ns and, if you can keep the load 
capacitance low enough, a maximum input frequency of > 1 GHz.

Always trying to learn....

Ed

On 8/20/2013 11:28 PM, Bruce Griffiths wrote:
> The same analysis applies however one would probably use something 
> like cascaded longtailed pairs with well defined gain (series emitter 
> feedback) and the low pass filter cap connected between the collectors 
> rather than opamps.
>
> Bruce
>
> Ed Palmer wrote:
>> Does anyone know if this situation would benefit from doing something 
>> similar to a 'Collins Hard Limiter' i.e. instead of squaring the 
>> signal in one stage, use maybe two or three cascaded stages with 
>> increasing bandwidths? Normally, Collins limiters are used with beat 
>> frequencies of less than 1 KHz, but maybe there's value in doing at 
>> typical time-nuts frequencies.
>>
>> Any thoughts?
>>
>> Ed
>>
>>
>> On 8/20/2013 10:02 PM, Said Jackson wrote:
>>> Hi Ed,
>>>
>>> For anything up to about 150MHz try the NC74SZ04 types from National 
>>> if you can find them NOS. they stopped making these years ago.. 
>>> Fairchild is ok too but not as fast from what I have seen.
>>>
>>> Forgot I wrote about it in 2009. Oh boy -age kicking in.
>>>
>>> Bye,
>>> Said
>>>
>>> Sent From iPhone
>>>
>>> On Aug 20, 2013, at 20:17, Ed Palmer <ed_palmer at sasktel.net> wrote:
>>>
>>>> Hi Said,
>>>>
>>>> Yes, I saw your message from 2009 where you warned about the sine 
>>>> waves.  That's why I was watching for it.  Thanks for the warning.  
>>>> I also realized that a DC Block and a 10 db attenuator makes a very 
>>>> nice TTL or CMOS to Wavecrest converter for anything except 1 PPS 
>>>> which would need about 15 db.  I tried an old circuit that uses an 
>>>> MC10116 ecl line receiver - it's actually a dead Racal Dana 1992 
>>>> counter where I'm using the processing on the external reference 
>>>> input to square up the signal.  It gives me a slew rate equivalent 
>>>> to about a 50 MHz sine wave.  It helped a lot, but not enough.  
>>>> I'll try a 74AC04 and a BRS2G Differential Line Receiver (risetime 
>>>> < 3ns, 400Mbps throughput).  Both are in my junkbox.
>>>>
>>>> Ed
>>>>
>>>>
>>>> On 8/20/2013 8:12 PM, Said Jackson wrote:
>>>>> Guys,
>>>>>
>>>>> The dts needs to be driven by square waves, driving them with sine 
>>>>> waves gives jitter values that are displayed significantly too 
>>>>> high due to trigger noise.
>>>>>
>>>>> Holzworth makes a small sine wave to square wave converter that 
>>>>> can drive 50 ohms. Use a DC block and an attenuator on the cmos 
>>>>> output to avoid damaging the dts inputs. You can make your own 
>>>>> converter using a single fast cmos gate, resistor, and blocking 
>>>>> cap. By using hand-selected gates I was able to achieve less 
>>>>> jitter with that circuit than what the Holzworth box was able to 
>>>>> achieve.
>>>>>
>>>>> Doing that conversion can bring down the measured rms jitter on a 
>>>>> very good 10MHz sine wave source from 10ps+ to less than 2ps - 
>>>>> basically at or below the noise floor of the dts.. Once you run at 
>>>>> the units' noise floor, you know your source is quite good..
>>>>>
>>>>> Bye,
>>>>> Said
>>>>>
>>>>> Sent From iPhone
>>>>>
>>>>> On Aug 20, 2013, at 18:51, Ed Palmer <ed_palmer at sasktel.net> wrote:
>>>>>
>>>>>> Adrian,
>>>>>>
>>>>>> I used Timelab to assess the reaction of the DTS-2077 to 
>>>>>> different sine wave inputs.  The differences in the noise floor 
>>>>>> are surprising.  The attached picture was made by taking the 
>>>>>> output of an HP 8647A Synthesized Generator through a splitter, 
>>>>>> and then through different lengths of cables to the inputs of the 
>>>>>> DTS-2077.  The combination of splitter and cable loss meant I 
>>>>>> couldn't get +7 dbm @ 1 GHz.  If I could have, the 1 GHz line 
>>>>>> might have been lower than it was.
>>>>>>
>>>>>> Ed



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